Sharif Digital Repository

One important problem in query optimization in centralized and decentralized databases is optimizing queries containing common sub-expressions, known as multi-query optimization. In processing these queries, the goal is to process a group of queries together and find a global execution plan with minimum cost for the query set. In most of researches which have approached this problem the focus were on exhaustive algorithms. Since size of the problem space for these algorithms grows exponential with query set size, these approaches are impractical. In this research we have presented six algorithms based on Ant Colony Optimization metaheuristic. We have compared the efficiency of these methods... 

By comparing the control systems, researcherstypically believe that the active systems of control have better performance than passive ones. However, the high costs and the required technology for their erection and maintenance have limited the use of active control systems. In order to improve the control system performance at lower costs, semi-active control systems were also considered. Their performance is based on creating the desired control force by changing the instrument characteristics.Moreover, recent researches have shown that the improved performance of these instruments in structures compared to passive control systems, are typically due to reducing the flexibility of the... 

Many offshore platforms as TLP, Semi-submersible and Spar are used for oil extraction and energy harvesting. One of the challenges of these structures is related to vibrations due to the environmental sea waves and wind loads. The optimal way for the response reduction of an offshore structure in heave direction is the installing of thin heave plate. The heave plate induces vortex shedding and pressure drop on fluid flow downstream. Diameter difference of heave plates in an array can improve the obtained damping and added mass for a given small spacing between plates, which has not been studied up to now. Hence, in the present thesis it was observed that converting of the uniform to... 

A Spirit of Trust results from Brandom's thirty-year effort to give a pragmatistic reading of Hegel's Phenomenology of Spirit. In A Spirit of Trust, Brandom reformulates Hegel's arguments in the language of contemporary Analytical Philosophy and gives a unique interpretation of Hegel's key concepts. In this Thesis, we will examine one of its key concepts, namely, Trust; We will pursue the following questions: First, What is Trust? And what is its connection to other aspects of Brandom's philosophy? Second, How does Trust help us in overcoming Alienation? Third, Are Confession and Forgiveness, which are the constitutive concepts of Trust, psychologistic or normative? Fourth, What is the... 

A tensile-compression ring is derived from the spoke wheel principle. The wheel is one of the greatest inventions in mankind. The use of the wheel has developed through time. Engineers found out that the use of the spoke wheel as a roof structure provides many benefits. With the spoke wheel principle a lightweight, cost-efficient roof structure can be made. In recent years the spoke wheel principle has also been applied for oval shaped roofs in order to increase the application of the principle. An example is the use of the roof structure for football stadia. The problem is that the spoke wheel principle will only work at full extend when its shape is completely circular. The question rises... 

In most countries Frequency control services as one of the Ancillary services are presented in market scheme. Frequency control are used in different levels to balance generation and demand. Each reserve levels is implemented with specific characteristics and rules. Clearance of energy and one control reserve has some drawbacks so in this thesis we try to clear energy and different reserve levels simultaneously. Each reserve level is determined with special criteria. This criterion in primary reserve is frequency deviation restriction and unit commitment risk in territory reserve that is determined by system operator. In this thesis these two criteria are formulated in linear form and... 

The increasing rate of population and agricultural development over the past few decades has led to a significant rise in the pollution of surface and groundwater. The application of animal and synthetic fertilizers containing phosphorus, which increases the levels of this element in the soil, can be considered one of the factors endangering the environment, especially the quality of surface waters. The transport of phosphorus, which is one of the pollutants in agricultural runoff, can lead to the degradation of aquatic ecosystems and reduce the quality and usability of water resources. Accordingly, various numerical models have been developed to simulate phosphorus loss from the soil. They... 

Identifying anomalous events is one of the vital topics in research as it often leads to the detection of actionable and critical information such as intrusions, faults, and system failures. With its importance, there has been a substantial body of work for network anomaly detection using supervised and unsupervised machine learning techniques with their own strengths and weaknesses. In this work, we take advantage of both worlds of unsupervised and supervised learning methods. The basic process model we present in this paper includes (i) clustering the training data set to create referential labels, (ii) building a supervised learning model with the automatically produced labels, and (iii)... 

The concept of "experience" plays a key role in modern philosophy. Experience is also the central concept of Adorno's philosophy. Adorno's claim is that the possibility of human experience in contemporary western society is facing limitations. From Adorno's point of view, experience has become objectified in the contemporary western world. Such a situation distorts the relationship between the subject and the object and distorts the experience. While describing the experience in the contemporary world, Adorno explains the conditions for the possibility of undistorted experience. According to Adorno, objectified relationships are reproduced in philosophical theories. Therefore, he seeks to... 

For both Fichte and Hegel, self-consciousness is an intersubjective concept; that is, for them, self-consciousness is necessarily constituted between, at least, two subjects. In Foundations of Natural Right, Fichte introduces summons and recognition as necessary conditions of self-consciousness, without which, i.e. an other who is calling upon the subject, the subject cannot be conscious at all. Hegel, in Phenomenology of Spirit, also says self-consciousness is desire which is satisfied only in another (self-) consciousness. Based on these ideas, I try to show that self-consciousness can be defined as having the both in view; the self (I) and the other (not-I), at the same time. In this... 

In recent years, the challenges of using fossil energy causes governments and researchers to focus on renewable energies. In this regard, one of the strategies for generating power is using wave energy converters. The aim of present study is modeling frequency and time domain analysis of the wave energy converter. the study focuses on the effect of Power-Take-Off system on the output power and efficiency under the Macoran sea waves. First, the concept of wave converters is explained and the commercialized ones are introduced. Then the related previous works are reviewed and the wave theories are briefly presented. In the following, a specified one-degree-of-freedom converter is modeled in... 

At the early stages of production, oil reservoirs may have enough energy to push the oil from the reservoir into the wellbore and subsequently from the wellbore to the surface. When the reservoir energy is too low for the well to flow, or the production rate desired is greater than the reservoir energy can deliver, using some kind of artificial lift method to provide the energy to bring the fluid to the surface, seems to be necessary. Continuous flow gas lift is one of the most common artificial lift methods widely used in the oil industry during which, at appropriate pressure, gas is injected in a suitable depth into the tubing to gasify the oil column, and thus assist the production. Each...